1. Field of the Invention
The present invention relates to a method for preparing cyclopropanecarboxylic, acids by acidolysis of the corresponding esters according to the following scheme: ##STR2## using an alkylbenzenesulfonic acid as the reaction catalyst, where
R.sub.1, R.sub.2, R.sub.3 are each, independently, H, C.sub.1 - to C.sub.4 -alkyl, or phenyl, PA1 R.sub.4 is H or COOR.sub.7, PA1 R.sub.5 is H, COOR.sub.7, or COOH, PA1 R.sub.6 is H, CH.sub.3, C.sub.2 H.sub.5, or C.sub.3 H.sub.7, PA1 R.sub.7 is CH.sub.3 or C.sub.2 H.sub.5. PA1 R.sub.1, R.sub.2, R.sub.3 are each, independently, H, C.sub.1 - to C.sub.4 -alkyl, or phenyl, PA1 R.sub.4 is H or COOR.sub.7, PA1 R.sub.5 is H, COOR.sub.7, or COOH, PA1 R.sub.6 is H, CH.sub.3, C.sub.2 H.sub.5, or C.sub.3 H.sub.7, PA1 R.sub.7 is CH.sub.3 or C.sub.2 H.sub.5, and PA1 m+n is 5 to 15.
2. Description of the Background
Cyclopropanecarboxylic acids are important intermediates in the preparation of a variety of asymmetric chemicals, pharmaceutical products and crop protection agents.
The cyclopropanecarboxylic acid esters (1) are prepared by known methods. The methyl cyclopropanecarboxylate is synthesized, for example, by reacting methyl 4-chlorobutyrate with sodium methylate, according to EP-A-0 577 949, incorporated herein by reference.
The literature also discloses syntheses of cyclopropanecarboxylic acids (3). For example, Org. Synth. Coll. Vol. 3 (1955), 221, describes the alkaline saponification of the corresponding nitrite. This method gives rise to ammonia and alkali metal salts as waste products in stoichiometric amounts, which have to be disposed of.
The alkaline saponification of cyclopropanecarboxylic acid esters likewise encounters the problem of salt being produced in stoichiometric amounts.
With acidolysis, in contrast, less salt is produced, since this method makes use of catalysis. Detailed descriptions of the acidolysis are found in textbooks, e.g. in Organikum, 20th edition, Johann Ambrosius Barth Verlag (1996), 459. This recommends sulfuric acid as the catalyst and formic acid as the carboxylic acid.
In the case of the cyclopropanecarboxylic acids, such acidolysis requires relatively large amounts of sulfuric acid. Furthermore, this acid has to be neutralized, for example with sodium hydroxide solution, after the reaction since the sensitive cyclopropanecarboxylic acids are otherwise decomposed when they are worked up by distillation. This procedure therefore likewise gives rise to quantities of salts which have to be separated off and disposed of.
All the known methods for preparing cyclopropanecarboxylic acids therefore have in common that they consume large amounts of chemicals, thus leading to waste disposal problems.